LACTOSE control scoring helps predict surgical outcomes for childhood intermittent exotropia

Objective: To determine whether preoperative Look And Cover, then Ten seconds of Observation Scale for Exotropia (LACTOSE) control scores can predict surgical outcomes in children with intermittent exotropia. Design: Retrospective interventional case series from a university-based tertiary eye care centre. Participants: A total of 350 patients with basic-type intermittent exotropia who underwent bilateral lateral rectus recession between 3 and 10 years of age from January 2014 to December 2017. Methods: All patients were preoperatively assessed for their degree of control at both distance and near according to LACTOSE scoring system. Demographic, clinical, and oculomotor data before and after surgery were collected and analyzed with regard to the degree of control. Surgical success was defined as an alignment between 10 prism diopters (PD) of exodeviation and 5 PD of esodeviation at both distance and near. Results: Younger age, lower visual acuity, worse stereoacuity, and larger angle of deviation were associated with higher (i.e., worse) LACTOSE control scores. Of the 350 patients having surgery, 169 (48.3%) were followed for more than 12 months postoperatively. Surgical success was achieved in 132 (78.1%) patients at 12 months after surgery. The only significant predictor of surgical success was preoperative LACTOSE score. There was a significant inverse relationship between LACTOSE scores and surgical success rates for both distance and near scores (p = 0.004 and 0.023, respectively). Conclusions: Higher distance and near LACTOSE scores representing worse control of deviation were associated with higher rates of surgical failure in children with intermittent exotropia. This finding indicates that surgical outcome of intermittent exotropia can be predicted by preoperative LACTOSE scores.